Various hot plate welding apparatus are known for fusing together heat weldable components and workpieces. Typically such devices incorporate a hot plate which by thermal contact melts part of the component and/or the workpiece to a partially melted or tacky state. After such partial melting, the component and workpiece are moved into physical contact and cooled, fusing together and forming the finished article.
Frequently such hot plate welders are used in the final production of blow molded thermoplastic products, such as plastic gas tanks and fluid containers as are used in automobiles or as brake, antifreeze and/or washer fluid reservoirs. Conventional hot plate welding systems typically incorporate a movable hot plate which is brought into bearing contact against the outer bottom, side or top wall (hereinafter collectively referred to as the sidewall) of a formed or molded workpiece to effect the partial melting of a contact surface to which a selected component is to be joined. Following the initial melting, the hot plate is then moved to a remote location, and the selected component, such as a plastic seal plug, filler neck, bracket, vent nipple, blow pin, or the like, is then moved against the contact surface to form the completed product.
While conventional hot plate welding systems have been successfully applied for many different applications, automotive fuel tanks manufactured from HDPE (High Density Polyethylene) have proved to be especially challenging. Low fuel vapor permeation requirements necessitate that the container wall be formed using multiple layers of plastic materials. An EVOH layer, which provides permeation reduction, is typically sandwiched between an inner and outer HDPE layer which are necessary for advantageous physical properties of the fuel tank. Additional layers are typically required so that the EVOH layer can properly bond to the HDPE layers. Ideally, to manufacture an end product with the lowest possible fuel vapor permeation the container wall formed in this fashion should not be disturbed by cutting a hole or any type of opening. However, typical fuel tanks have at least a fill opening and an opening for the fuel delivery module which cannot be avoided, as well as other openings for vent valves and similar type of valves. If additional valves are required one way to avoid having to first cut an opening before welding the valve to the tank sidewall is to attach the valve to the inside of the container.